The present invention relates to a switching circuit and more particularly but not exclusively to a switching circuit for an output node.
In integrated circuits there often exists a need to switch a circuit node from a first state, or voltage level, to a second state, or voltage level. There are known circuits which have been provided for providing such a switching function. However it is often found that the speed of switching of these known circuits is unsatisfactorily show and also unacceptable switching currents are present.
It is an aim of embodiments of the present invention to provide a switching circuit which mitigates against the disadvantages of known switching circuits.
According to the present invention there is provided a switching circuit for an output node comprising: pull-up circuitry connected to said output node and an upper supply voltage node, said pull-up circuitry having control circuitry for causing said pull-up circuitry to supply a pull-up current to said output node; a switch connected between said output node and said pull-up circuitry, said switch being responsive to a voltage at said output node whereby said switch is rendered non-conductive when said output node is at a voltage substantially equal to said upper supply voltage; pull-down circuitry connected to said output node and a lower supply voltage node for supplying a pull-up down current to said output node, whereby when the voltage at said output node falls said switch becomes conductive, wherein said control circuitry substantially terminates operation of said pull-up circuitry while said switch is non-conductive.
According to the present invention there is also provided a method of switching an output node comprises: controlling a pull-up circuit to supply a pull-up current to said output node; sensing a voltage at said output node and in response to said voltage being substantially equal to an upper supply voltage, rendering non-conductive a switch disposed between said pull-up circuit and said output node; while said switch is non-conductive, substantially terminating operation of said pull-up circuit, and initiating operating of a pull-down circuit to supply a pull-down current to said output node whereby said voltage falls and said switch becomes conductive; and thereafter completing pull-down of said output node.
According to the present invention there is further provided a method of switching an output node comprising: controlling a pull-down circuit to supply a pull-down current to said output node; sensing a voltage at said output node and in response to said voltage being substantially equal to a lower supply voltage, rendering non-conductive a switch disposed between said pull-down circuit and said output node; while said switch is non-conductive, substantially terminating operation of said pull-down circuit, and initiating operation of a pull-up circuit to supply a pull-up current to said output node whereby said voltage rises and said switch becomes conductive; and thereafter completing pull-up of said output node.
To provide a better understanding of the present invention a preferred embodiment will now be described in further detail by way of example with reference to the following Figures, in which;